Kαyields from Ti foils irradiated with ultrashort laser pulses

We have studied the emission of $K\alpha$ radiation from Ti foils irradiated with ultrashort (45 fs) laser pulses. We utilized the fundamental (800 nm) light from a Ti:sapphire laser on bare foils and foils coated with a thin layer of parylene E (CH). The focusing was varied widely to give a range of intensities from approximately ${10}^{15}–{10}^{19}\mathrm{W}{\mathrm{cm}}^{-2}$. Our results show a conversion efficiency of laser to $K\alpha$ energy of $\sim {10}^{-4}$ at tight focus for both types of targets. In addition, the coated targets exhibited strong secondary peaks of conversion at large defocus, which we believe are due to modification of the extent of preformed plasma due to the dielectric nature of the plastic layer. This in turn affects the level of resonance absorption. A simple model of $K\alpha$ production predicts a much higher conversion than seen experimentally and possible reasons for this are discussed.